This is an open access title available under the terms of a CC BY-NC-ND 4.0 International licence. It is free to read on the Oxford Academic platform and offered as a free PDF download from OUP and selected open access locations. In Shared Rule in Federal Theory and Practice, Sean Mueller provides a new, in-depth treatment of shared rule, a crucial but so far largely neglected dimension of federalism and multilevel governance. He discusses shared rule's conceptual evolution and defines three different meanings commonly ascribed to it: shared rule as horizontal cooperation, centralization, or bottom-up influence seeking. An original expert survey conducted among 38 federalism scholars in 11 countries is used to measure actual regional government influence over national decisions. Drawing on a wide range of literature, from lobbying and political parties to power sharing and secessionism, the author then investigates the emergence and impact of shared rule thus understood. The evidence presented includes qualitative case studies on Belgium, Canada, Germany, Spain, Switzerland, and the US as well as quantitative, cross-sectional analyses at regional and national level. Mueller shows that shared rule has the potential to become the holy grail of territorial politics in that it satisfies both those wanting greater unity and uniformity of policy making as well as those desiring greater regional autonomy and recognition of diversity. Building on the conceptual and empirical groundwork laid by the Regional Authority Index, he takes us further and deeper still into the mechanics of territorial contestation, cooperation, and cohesion. Transformations in Governance is a major academic book series from Oxford University Press. It is designed to accommodate the impressive growth of research in comparative politics, international relations, public policy, federalism, and environmental and urban studies concerned with the dispersion of authority from central states to supranational institutions, subnational governments, and public-private networks. It brings together work that advances our understanding of the organization, causes, and consequences of multilevel and complex governance. The series is selective, containing annually a small number of books of exceptionally high quality by leading and emerging scholars. The series is edited by Liesbet Hooghe and Gary Marks of the University of North Carolina, Chapel Hill, and Walter Mattli of the University of Oxford.